Sealed motor rotor with ball bearing

ABSTRACT

The disclosure relates to an electric motor including a support block containing a ball bearing housing, a rotor that projects from this housing, and a stator assembly mounted around said rotor and fastened on said support block, characterized in that an annular seal, preferably of O-ring type, is squeezed between said stator assembly and the periphery of the fixed race of said ball bearing, the pressure of said annular seal preventing axial and rotational movement of said fixed race; the invention also proposes an assembly process for such an electric motor. The invention is notably suitable for sealed rotor motors.

The invention mainly relates to sealed rotor motors for applications inwhich it is required to avoid contact between the stator of the motorand a dangerous liquid or gaseous environment.

A typical example of the application of such a motor is the control of avalve that shuts off the flow of gas to a boiler. The electrical partsof the motor (in practice the stator) must not be in contact with thegas. There are of course many other applications of such motors.

These motors are often constructed in the following manner: a rotorassembly equipped with a ball bearing is mounted in a massive supportblock that forms a partition separating the rotor environment from thestator environment. The ball bearing is mounted in a housing in thissupport block with the rotor projecting outside the housing. A statorassembly is mounted around the rotor and is fastened to the supportblock by screws, for example.

The present invention notably concerns the fitting of the ball bearingin the support block.

Since the invention is advantageously (though not exclusively)applicable to sealed rotor motors, before indicating the object of theinvention, we shall also explain how the invention provides for sealingof the motor.

In a sealed rotor motor, it is necessary to separate the environment onthe rotor side from the environment on the stator side and prevent forexample any flow of gas via the ball bearing or via the air gap betweenthe rotor and stator. To do this, a sealing bell is used to enclose thewhole rotor assembly. The lateral, cylindrical, nonmagnetic wall of thisbell is inserted into the rotor/stator air gap. The whole statorassembly, notably including the conductors feeding the stator, islocated outside the bell. The bell also makes sealed contact with thesupport block, in other words with the solid wall separating the statorenvironment from the rotor environment, thereby ensuring that the twoenvironments are separated from each other in a gas-tight manner. Thebell encloses not only the rotor but also the ball bearing.

The invention proposes a particular way of mounting the ball bearing inthe support block that is notably suitable for sealed rotor motors.

The ball bearing fits in the housing provided in this support block; thehousing diameter is adjusted so that the bearing can be hand-fitted inthe housing tightly but without friction. In prior art solutions theball bearing was force-fitted; in some solutions in which it washand-fitted a metal tongue or other means was necessary toimmobilize-rotationally and axially—the fixed bearing race in thehousing.

In the present invention, the fixed bearing race is immobilized by meansof an elastic annular seal, preferably of O-ring type, inserted betweenthe stator assembly of the motor and the periphery of the fixed race andcompressed by the fastening of the stator assembly on the support block.

Once the ball bearing has been hand-fitted into the support block, withthe rotor projecting outside this housing, the stator assembly ismounted around the rotor then fixed onto the support block, in generalby screws, which also squeezes the annular seal against the fixed raceof the bearing. This pressure also holds the bearing firmly in itshousing, and the friction of the seal prevents the fixed race fromrotating under the influence of the rotation of the rotor.

The invention is therefore an electric motor including a support blockcontaining a ball bearing housing, a rotor that projects from thishousing, and a stator assembly mounted around said rotor and fastened onsaid support block, characterized in that an annular seal, preferably ofO-ring type, is squeezed between said stator assembly and the peripheryof the fixed race of said ball bearing, the pressure of said annularseal preventing axial and rotational movement of said fixed race.

In the case of a sealed motor including a bell that encloses the rotor,the open end of the bell is bent radially outwards to form a rim (whoseplane is therefore parallel to the plane of the annular seal) which isinserted between the stator assembly and the annular seal. This rim ofthe bell is held pressed against the seal by the tightening of thestator assembly on the support block. The seal bears not only on theperiphery of the fixed bearing race (but without making a seal at thispoint), but also on part of the support block, which ensures sealingbetween the bell and the support block around the periphery of the bell.

The ball bearing housing preferably has, on the side on which thebearing is inserted, a peripheral section of diameter slightly greaterthan that at the bottom of the housing which holds the fixed bearingrace, said seal being fitted in this wider section, the diameter andradial thickness of the seal being chosen such that the periphery of theseal presses against the internal cylindrical wall of this widersection.

With the arrangement of parts according to the invention, the bearing isnot subjected to any excessive forces, which avoids any risk ofdeformation and enables optimal operation.

The degree of compression of the seal enables dimensional variations ofthe various parts to be taken into account in the presence of largetemperature gradients, in order to ensure that the bearing remainsfirmly immobilized despite these temperature variations.

In the case of a sealed rotor motor the invention also provides forsealing.

Finally, the invention also includes an assembly process for theelectric motor, including the following steps: preparation of a rotorassembly including a rotor and a ball bearing; fitting of this assemblyin a ball bearing housing in a support block, with said rotor projectingoutside the housing; fitting of an annular seal, preferably of O-ringtype, against the fixed race of said ball bearing; fitting of a statorassembly around the rotor; and tightening of said stator assemblyagainst said support block, this tightening squeezing said annular sealagainst said fixed race. For a sealed rotor motor, said stage of fittingof the stator assembly is preceded by a stage of fitting of a nonmagnetic sealing bell around said rotor, said bell having a rim bentradially outwards that presses against said annular seal and said statorassembly pressing against this rim to press it against said annularseal.

The invention will be better understood and other characteristics andadvantages will become clear on reading the following detaileddescription of a preferred embodiment, given only as a non-limitativeexample, with reference to the attached drawings of which:

FIG. 1 shows a general view of an embodiment of motor according to theinvention;

FIG. 2 shows a detailed enlarged view of the fitting of the ballbearing.

The invention will be described taking the example of a sealed steppingrotor motor used to control a gas flow control valve feeding a boilergas. However, other applications are possible.

The stepping motor is mounted on a massive support block 10 which formsa partition separating the gas-filled environment from the externalenvironment. The body of the valve controlled by this motor is not shownin the figure. The valve is controlled via a shaft or rod 14 that canmove longitudinally. The body of the solenoid valve encloses the end ofthe rod 14 and is closed by the face of the support block 10 on theright side of FIG. 1.

The role of the motor is to drive the rod 14 longitudinally, for exampleto open or close an aperture (not shown in the figure).

The massive support block 10 includes a transversal part 20 in form of aflange (hereinafter referred to as the “flange 20”) on which the valvebody and motor stator can be fixed, respectively on the right and on theleft of the flange 20. This support block 10 has an axial hole to allowthe rod 14 to penetrate it.

The actual electric motor is essential composed of a stator assembly 24,a rotor 26, and a ball bearing 28. The stator assembly and the rotor aremounted on the left of the flange 20 in the figures. The ball bearing isfitted in a housing 30 in the flange 20. The rod 14 extends on bothsides of the flange 20, via a hole in the bottom of this housing 30.

The rotor is preferably composed of permanent magnets 27 distributedaround the periphery of a rotor body preferably made of plasticmaterial.

The stator includes pole pieces 40 enclosed in electrical coils 42which, when mounted, face the rotor composed of permanent magnets. Thisrotor zone is located outside the support block 10 (on the left of thefigures).

Along part of its length the rod 14 is threaded on the outside; thisthreaded section engages corresponding threads on the inside of therotor. Means (not shown) are provided to prevent rotation of the rod 14so that, when the rotor turns, the rod 14 moves longitudinally but notrotationally.

The stator assembly 24, constituted by the pole pieces 40, coils 42,lateral fastening flanges 44, a cylindrical band 46, and a mountingplate 48, is fastened on the flange 20 using screws 50. These screwshold the plate 48 against the flange 20.

The screwing of the mounting plate 48 on the flange presses an annularseal 60, preferably of O-ring type, into the housing 30 of the ballbearing, thereby pressing the ball bearing fully into the housing.

For a sealed rotor motor, as shown in the figures, a sealing bell 62 isprovided to cover the whole rotor in order to separate it from thestator and assure gas-tightness between the rotor environment and thestator environment.

This bell 62 has a cylindrical wall that fits between the pole pieces ofthe stator and the permanent magnets of the rotor. It is thin and madeof nonmagnetic metal (preferably stainless steel) or plastic, so that itcan be inserted in the rotor/stator air gap without affecting theelectromagnetic operation of the motor. The top of the bell, on the leftin the figure, encloses the end of the rotor. The open end of the bellis bent radially outwards, parallel to the transversal flange 20 to forma rim 80 that presses against the seal 60. The plane of this rim istherefore parallel to the plane of the annular seal, in other wordsperpendicularly to the axis of rotation of the rotor. The rim 80 issandwiched between the mounting plate 48 of the stator and the seal 60,such that the tightening of the plate 48 onto the flange 20 presses therim of the bell onto the seal which in turn presses the ball bearing 28into its housing.

FIG. 2 shows an enlarged view of the bell 62, the seal 60 and the ballbearing 28. The housing 30 of the ball bearing is in the form of acylindrical recess with two different diameters, the first diameter atthe open end of the housing being slightly larger than the seconddiameter at the bottom of the recess. The first diameter accommodatesthe seal 60, the second accommodates the ball bearing. The ball bearingbears against the bottom of this housing 30 in which there is a hole toallow passage of the rod 14.

The ball bearing 28 includes a fixed race 70 (which does not turn whenthe rotor turns) and a mobile race 72 that turns under the action of therotor. The mobile race 72 is crimped on the rotor body (ultrasoundcrimping in the case of a plastic body). The nominal external diameterof the fixed race is equal to the nominal internal diameter of thenarrower section of the housing, the machining tolerances being chosento enable hand-fitting of the bearing in the housing.

When the rotor assembly with its rod 14 and its ball bearing 28 isinserted in the housing containing a hole to allow passage of the rod14, the ball bearing slides snuggly without friction into the narrowersection of the housing. The seal 60, preferably of O-ring type, is thenplaced in the wider section of the housing 30. The external diameter ofthe seal (uncompressed) corresponds substantially to the internaldiameter of this section of the housing; this external diameter of theseal increases when the seal is compressed towards the bottom of thehousing. The seal makes a gas-tight seal on the internal cylindricalwall of the wider section of the housing 30.

The internal diameter of the O-ring is chosen to ensure a certainthickness of the O-ring in the radial direction, such that the sealbears only on the fixed race 70 of the bearing, but not other parts ofthe bearing.

Next, the bell 62 is fitted on the rotor. Its rim 80 fits inside thewider section of the housing 30 and presses on the seal. Then the statorassembly, mounted on its mounting plate 48, is fitted around the bell.Finally, the plate 48 is screwed onto the flange 20, which squeezes therim 80 of the bell against the seal 60. This compresses the seal makingit press axially on the fixed race 70 (thereby pressing the wholebearing assembly fully into its housing 30) and also radially againstthe lateral cylindrical wall of the wider section of the housing 30.

The rim of the bell preferably fits snuggly inside the housing 30, butit is the contact of the seal against the bell rim and against the wallof the housing that assures the gas-tightness and prevents any leakageof gas from one side to the other of the flange 20 via the orificethrough which the rod 14 passes and notably via the ball bearing. Thebell 62 confines the gas around the rotor, preventing it from passing tothe stator and, more generally, preventing the gas reaching the exteriorof the flange (on the left in the figures).

As we see in FIG. 2, the mounting plate 48 preferably includes at thelevel of the rim 80 of the bell 62, a shallow cylindrical shoulder whosediameter is the same diameter as the wider section of the housing 30.This shoulder engages in the housing 30 to assure perfect centering ofthe bell rim against the seal 60 in the housing 30.

The preceding description relates to a method of fitting a ball bearingthat is particularly suitable for sealed rotor motors. However, it willbe clear to professionals of the art that the invention has otherapplications.

What is claimed is:
 1. An electric motor comprising: a support blockhaving a ball bearing housing containing a ball bearing including astatic race and a rotating race; a rotor projecting from said housing onone side of said support block, and a rotor shaft traversing saidhousing, said rotating race, and said support block; a stator assemblymounted around said rotor on said one side of the support block andfastened on said support block; an annular seal squeezed between saidstator assembly and a periphery of said fixed race of the ball bearing,a pressure of said annular seal against the fixed race preventing axialand rotational movement of said fixed race; and a sealing bell sealinglysurrounding said rotor on said one side of the support block, saidsealing bell having a non-magnetic cylindrical portion interposedbetween said rotor and said stator assembly and having a rim bentradially outwards and inserted between said stator assembly and saidsupport block, said rim being held pressed against said annular seal bythe fastening of said stator onto said support block; wherein the bellsealingly separates a first space portion containing the rotor from asecond space portion containing the stator.
 2. A motor according toclaim 1, wherein said annular seal presses against a part of saidsupport block to improve the sealing between said first and second spaceportions.
 3. A motor according to claim 2, wherein said ball bearinghousing comprises on a side on which the bearing is inserted, aperipheral cylindrical recess having a diameter slightly greater thanthat of said fixed bearing race, said annular seal being fitted in therecess of said housing, a diameter and a radial thickness of saidannular seal being chosen such that the periphery presses against aninternal cylindrical wall of the recess.
 4. A motor according to claim3, wherein said stator assembly comprises mounting plate bearing againstsaid support block, and pressing said rim of said bell against saidannular seal, and the mounting plate having at the position of said rima shallow cylindrical shoulder with a diameter corresponding to therecess diameter of said housing, the shoulder engaging in said housingwhen said stator assembly is fitted.
 5. The motor according to claim 1,wherein the annular seal comprises an O-ring type seal.
 6. An assemblyprocess for an electric motor comprising: preparing a rotor assemblyincluding a rotor and a ball bearing; fitting the rotor assembly in aball bearing housing in a support block, with said rotor projectingoutside the housing on a first side of the support block, with a shaftof the rotor projecting on an opposite side of the support block throughsaid ball bearing housing; fitting an annular seal against a fixed raceof said ball bearing; fitting a stator assembly around the rotor; andtightening said stator assembly against said support block to squeezesaid annular seal against said fixed race.
 7. The assembly processaccording to claim 6, wherein said fitting of the stator assembly ispreceded by fitting a non magnetic sealing bell around said rotor, saidbell having a rim bent radially outwards that presses against saidannular seal and said stator assembly.
 8. The assembly process accordingto claim 6, wherein the annular seal comprises an O-ring type seal.